JR 8711 vs. Hitec 7955

[50%plane]

Has anyone tested the actual torq values of the 8711's and 7955's?

Thanks,
Chris

[Tin man]

	Quote: Originally Posted by 50%plane
	Has anyone tested the actual torq values of the 8711's and 7955's? Thanks, Chris

See here:
http://troybuiltmodels.com/newsite/p...omparison.html

7955: 248 oz/in drawing 2.7 amps

8711: 344 oz/in drawing 4.5 amps


--
But

[rcairflr]

	Quote: Originally Posted by Tin man
	See here: http://troybuiltmodels.com/newsite/p...omparison.html 7955: 248 oz/in drawing 2.7 amps 8711: 344 oz/in drawing 4.5 amps -- But

I believe TBM just copied and pasted the same numbers from the 5955 onto the 7955. There was someone here on FG that did a comparison of the 5955 to the 7955 and the 7955 had 15-20% more power than the 5955.

[50%plane]

	Quote: Originally Posted by rcairflr
	I believe TBM just copied and pasted the same numbers from the 5955 onto the 7955. There was someone here on FG that did a comparison of the 5955 to the 7955 and the 7955 had 15-20% more power than the 5955.

Do you have a link to that?

[rcairflr]

I'll find it, just need some time... Also a take a look at the new Airtronics 94780M rated at 423 in/oz at 6V. I just installed one on the rudder of my 35% QQ Yak.

[rcairflr]

Here is a post I did awhile back that I copied and pasted. The comparison between 5955 and 7955 was done by KrisW


Since Mike Mayberry invited us to do our own "testing" I just thought I'd pass along the results of soem tests I just ran on the bench.

Basically I compared, head-head, a Hitec 5955 to a 7955, for overall power and torque at 3 stages of heating . .Dead cold. . warmed up. . allowed to cool with an ice cube laying on the heatsink, but left running, for 1 minute (to test the sdrvos heat recovery capability). All tests were done for how much weight the servo could pull against gravity, as the arm traversed past 90 degrees, giving a "moving torque", and then as it stalled at about 90 degrees with a heavier load.

The test rig had the servos facing eachother, using a clevis from which a 4-40 rod hung, that hooked to a canister that I loaded with lead weights. The weight of the entire load was also verified using a 1/2lbs increment digital scale (8 ounces) I used the stock, as shipped 7/8" arms, then transposed the readings to what they would be using a 1" arm (basically reduce the load weight attained by 14%, or 1/7, because a 1" arm is 1/7 longer)

Voltage was supplied by a 2s1p Li-Ion pack from Fromeco, then regulated through a Fromeco 10 amp regulator set to 6 vdc output, and monitored to make sure the voltage stayed steady throughout the tests (it did). this went to a JR 2100 synthesized receiver, all 3 outputs from the regulator into the ports of the receiver, and the servoes run off a "y" from the Throttle channel, with movement end points set to 150% movement (900-2100 msec of pulse width range. . center at 1500msec)

Basicaly, the weighted basket sat on a stand, with 1/8" clearance between the pull rod and the handle of the basket, and then aplied load as it was lifted while the servo arm traversed. Load began being applied at approximately 30 degrees off midpoint of traverse across horizontal.

Here's the results from the two servos. Traverse means the servo may have struggled, but it made it past 1/2 throw and kept going. Stall means it stalled at 90 degrees, or parallel to the ground. First number is for the 5955, second is for the 7955.

5955 . . . . . . . . . . . . . . . .7955

Startup, Stall: 320 ounces. . . . 340 ounces

Warmed up for 1 minute, no load, Then:
traverse Center: 230. . . . . . 300
Stalls at: 260 ounces. . . . . . 320 ounces

Cooled, traverse: 260. . . . . . 335
Cooled, Stalls: 270. . . . . . 350

Now, I'll be the first to say this was NOT a scientific test donein a laboratory, but the 7955's consistently out-torqued the 5955's by 10-15% once warmed up, and handily beat any readings I have seen published for the 5955's elsewhere on the Net. nly time will tell if the new Motor and amplifier design hold up to the rigors of flying hard with oversized control surfaces, but I am thoroughly satisfied that the 7955's are a definite improvement in consistency and overall torque after the servo warms up a bit.

As for centering, hitting end points, etc etc etc. The 7955 was much tighter under load and more consistent on hitting the same point (within 2 degrees) time after time, with a 150 ounce load on the arm. Centering was also more consistent. Whereas the 5955 might be off a degree depending on which direction you approached center from, the 7955 did not seem to have this issue, and was consistently dead on when centered. No load and centering were indistinguishable tome, but loaded the 7955 definitely outshined it's older brother.

I'd say, personally, that HiTec has hit a big time home run with this one .. and at the low price they are currently being offred by Servo City and other vendors, I suggest stocking up NOW. . Great Servo. . I bought 5 this time . .5 more will be here inside a month. . now what to do with all these 5955's. . . . . . .
__________________
KrisW
"Mediocrity is doing it THEIR way"

[50%plane]

Kool! Thanks. 198:

I guess the 7955 and 8711 are similar with the 8711 possibly having a slight edge...

[Kripto]

	Quote: Originally Posted by rcairflr
	I'll find it, just need some time... Also a take a look at the new Airtronics 94780M rated at 423 in/oz at 6V. I just installed one on the rudder of my 35% QQ Yak.

What servo arm you use, you use the servo pull pull?

[rcairflr]

Glued the existing arm to the QQ rudder arm and then secured with 2 4-40 screws.

[Tin man]

	Quote: Originally Posted by 50%plane
	Kool! Thanks. 198: I guess the 7955 and 8711 are similar with the 8711 possibly having a slight edge...

If the 7955s really are that much better than 5955s than I'd rather go with 7955 over 8711. But I'm tired of the JR slop.

I'd also like to know, if the 7955 really is better, why HiTec lists the specs as the same as 5955. Seems they'd want to promote that.



--
Mike

[rcairflr]

My feelings are they overrated the 5955 and now the 7955 are accurately rated.
I agree with you on the 8711, I have one on the rudder of a 35% Extra, I'm getting ready to send it back to Horizon for the 2nd time. Jitters like crazy at the center position until you put your hand on it, then it stops. That's why I'm trying the Airtronics 94780.

[Tin man]

	Quote: Originally Posted by rcairflr
	My feelings are they overrated the 5955 and now the 7955 are accurately rated. I agree with you on the 8711, I have one on the rudder of a 35% Extra, I'm getting ready to send it back to Horizon for the 2nd time. Jitters like crazy at the center position until you put your hand on it, then it stops. That's why I'm trying the Airtronics 94780.

Yep, seen it enough times to know it ain't a myth. I've read how it's OK to fly if the jitter stops if you touch the control surface, but I have a problem flying with a servo hunting for center. Some say that it's the pot, and you can mitigate it by moving the arm one "click" on the shaft, and then re-centering via sub-trim. That will cause the pot to have a new center, where it spends most of its time (and, according to the theory, wears at that spot--which means it has to hunt for it if it's at center).

But the pot theory doesn't explain it all. I can feel the slop when the servo isn't even on, so gear-train is an issue too (or instead). I also run a single 8711 in a 35% (CARF Extra SX), which I am trying to keep as light as possible. That servo is brand-new and boy is it nice to not have any slop--at least for now. Be interesting to hear how that Airtronics holds up.

As for why HiTec is not promoting the 7955 as that much better than the 5955, I was gonna write that it might be 'cause they were trying to make the specs more in touch with reality. I just couldn't see a corporation doing something like. But you never know...



--
Mike

[RCFree]

Slightly off the main theme of this thread, but to get a little more oomph, has anyone used the Hitec robotic servo "5990" which is rated like the 7955 at 6 volts, but will accept 7.4 volts and is rated at 416 in-oz at the higher voltage. The speed at 7.4 volts is 0.14 sec. Is this a reasonable choice for that husky rudder servo (7.4 volts would also mean - no voltage regulator needed)? I'd appreciate some feedback.

Ron

[Tin man]

I run now-discontinued 5995s, robotic servos, in my 40% comparf MX2. I run them at 6.4 volts and they work well (Turbo Reg).

However, it is my understanding that Hitec lists them at 7.4 volts because of their intended usage (i.e., not in a plane). In other words you can run a 5955 at 7.4 volts and get the same increase in tq/speed. But the life of the servo will be diminished, hence that voltage is not recommended for flying (but many do so nonetheless).


--
Mike

[sinergy]

edit - nm just looked at the date